Abstract Mitochondrial dysfunction is associated with ageing as well as a number of age-related neurodegenerative diseases including Alzheimer?s Disease (AD). Early onset AD has been linked to mutations in amyloid precursor protein (APP) and presenilins 1 and 2 (PS1 and PS2), which result in abnormal cleavage of APP and release of toxic amyloid beta (A?) peptides. Accumulating evidence suggests that APP intracellular domain (AICD) may also contribute to pathogenesis of AD. To gain insights into the normal and pathological roles of AICD, we previously used a biochemical affinity proteomic strategy and found that AICD directly interacts with a novel mitochondrial protein, Nipsnap1 (4-nitrophenyl phosphatase domain and non-neuronal SNAP-25 like protein homolog1). Although Nipsnap1 is evolutionarily conserved, very little is known about its function. Our long-term goal is to investigate the molecular and cellular function of Nipsnap1 and to determine its role in neurodegeneration. Toward this end, we generated a mouse with a targeted disruption of the Nipsnap1 gene. Disruption of Nipsnap1 expression profoundly affects intermediate metabolism and significantly increased apoptosis and neurodegeneration in the brain. Protein structure modeling and virtual ligand screening suggested that Nipsnap1 may bind to NADH and NADPH. Using in vitro biochemical assays, we found for the first time that Nipsnap1 directly binds to both NADH and NADPH. Moreover, we found significantly lower NAD+/NADH ratios in Nipsnap1 deficient brain. The balance between NAD+ and NADH is critical for production of ATP, maintenance of mitochondrial potential and regeneration of reducing agents within cells to counteract reactive oxygen radicals. Based on these preliminary results, we hypothesize that Nipsnap1 plays an important role in neuronal survival by modulating dehydrogenase activities and NAD(P)H levels. In this project, we will use biochemical approaches and primary neuronal cultures derived from WT and Nipsnap1 deficient mice to determine if: 1) Nipsnap1 interacts with and regulates multiple dehydrogenases in the mitochondria; 2) AICD interaction with Nipsnap1 affects dehydrogenase activity and neuronal NAD+/NADH levels. Our work will provide insights into the molecular function of Nipsnap1 and possibly a new mechanism by which AICD produces neurotoxicity.